We have been using several of their products for some time, with no problems at all so far! They are very easy to work with in terms of getting support tickets resolved quickly - both internally or via our account manager (we're part way through implementing them as well).
Their billing system isn't perfect but they've listened carefully when we asked questions about it during implementation; I'm sure this will improve over time too though :) Would definitely recommend working together if you need help understanding how things should be billed etc., otherwise there's nothing not enough praise here either :D.